To begin with, while mainly referring to FIGS. 7-10, descriptions are given regarding the configuration of a conventional inverter.
Additionally, FIG. 7 is a schematic main circuit diagram of a conventional inverter.
Moreover, FIG. 8 is a schematic external-appearance view of a conventional inverter module with two elements inside.
Moreover, FIG. 9 is a schematic section view of a conventional inverter module with two elements inside.
Moreover, FIG. 10 is a schematic inner part equivalency-circuit diagram of a conventional inverter module with two elements inside.
The inverter which is shown in FIG. 7 comprises an alternate current electric source 101 for commercial use, a diode rectifier module 102 which converts an alternate current to a direct current, a condenser 103 of large capacity, a load 104 such as a 3-phase motor or the like which has the U phase, V phase and W phase electrodes, and an inverter module 105 which possesses semiconductor elements for electric power such as IGBT (Insulated Gate Bipolar Transistor) chips 106, FWD (Free Wheel Diode) chips 107 and the like and converts a direct current to an alternate current.
The FWD chip 107 is connected with the IGBT chip 106 in reverse-parallel, and the inverter module 105 is configured with these of 6 arms (6 circuits).
Usually, for the inverter module 105, either two elements of the upper and lower arms are allowed to constitute one group, or six elements are allowed to constitute one group.
Hence, in a case where the inverter is configured, either three inverter modules with two elements inside are connected in parallel and made use of, or an inverter module with six elements inside is made use of as it is.
The inverter module with two elements inside which is shown in FIG. 8 comprises a P output electrode (a positive side electric-source-electric-potential output electrode) 108 of direct current and an N output electrode (a negative side electric-source-electric-potential output electrode) 109, a U output electrode 110 which is connected to the load side, and gate terminals 111 and 113 of the IGBT chips of the upper and lower arms and emitter terminals 112 and 114.
And, the inverter module with two elements inside which is shown in FIG. 9 comprises a copper base substrate 115, a ceramic substrate 116 for insulation, copper patterns 117, 118 and 119 for wiring and semiconductor chip connecting, IGBT chips 120 and 121 of the upper and lower arms, electrodes 122 and 123 for connecting the IGBT chips 120 and 121 and the copper patterns 118 and 119 respectively, and copper electrode bars 124, 125 and 126 for connecting the copper patterns 117, 118 and 119 and the P, U and N output electrodes respectively.
Additionally, it is similarly equipped also with FWD chips (not shown in the figures) as well as the IGBT chips 120 and 121.
As shown in FIG. 10, an inductor 127 gives the inductance L1 between the collector terminal of the upper arm and the P output electrode, an inductor 128 gives the inductance L2 between the emitter terminal of the upper arm and a connecting point 129, namely between the copper pattern 118 (refer to FIG. 9) and the copper electrode bar 125 (refer to FIG. 9), an inductor 130 gives the inductance L3 between the connecting point 129 and the collector terminal of the lower arm, and an inductor 131 gives the inductance L4 between the emitter terminal of the lower arm and the N output electrode.
Next, while mainly referring to FIG. 11, descriptions are given regarding the action of a conventional inverter.
Additionally, FIG. 11 is a schematic waveform chart of turn-off waveform of the IGBT of a conventional inverter module.
Usually, in the circuit of an inverter such as the above-mentioned, the operation thereof is performed with the IGBT allowed to be switched roughly at 10 kHz.
Represented as in the next equation is the peak electric voltage VCE(peak) (hereinafter simply the electric voltage VCE) which is applied between the collector terminal of the IGBT chip and the emitter terminal at the time when the IGBT is turned off.VCE=Ed+(L1+L2+L3+L4)·di/dt  (Equation 1)
Here, Ed is the direct current electric voltage of the condenser 103 (refer to FIG. 7), and di/dt is the magnitude of the changing rate (<0) of the electric current IC of the IGBT chip.
As shown in FIG. 11, the waveforms of the electric voltage VCE and the electric current IC of the IGBT chip largely change at the time when the IGBT is turned off.
Namely, the surge electric voltage ΔV(=VCE−Ed) which is the changing from the direct current electric voltage Ed is determined by the values of L1 through L4 and di/dt and, as is apparent from (Equation 1), if the values of L1 through L4 are large, then the electric voltage VCE becomes high which is applied at the time when the IGBT is turned off.
Because of this, chips whose electric voltage resistance-quantities are high often become necessary as the IGBT chip and the FWD chip that is connected in reverse-parallel, which is apt to lead to enlargement of the inverter module and cost increase, since a chip like that usually has a broad chip area.
Further, if the surge electric voltage is high, then the noise that is brought to the outer part is large, which is apt to lead to malfunction of an external instrument.
Now, if the copper electrode bars like the above-mentioned are allowed to come in close proximity to each other, then a phenomenon such that inductance components are made to cancel out by mutual inductance is generated.
Thereupon, known is an art such that the copper electrode bars, which are connected to the P, U and N output electrodes of the inverter module respectively, are allowed to come in close proximity to each other and are disposed above the upper faces of the chips so as to lower unnecessary inductance components by mutual inductance (for example, refer to Specification of Japanese Patent No. 4277169).